Cobalt metal has been produced by reduction of cobaltous oxalate. Cobaltous oxalate is generally produced by precipitating a solution of cobaltous chloride with oxalic acid or ammonium oxalate. By means of filtration, the cobaltous oxalate is separated from the liquor and washed in water. After drying, the cobaltous oxalate is pyrolysed in a reducing atmosphere at about 500.degree. C. to produce the cobalt metal powder. Impurities in the metal powder are due to the impurities in the cobaltous oxalate which come from the cobaltous chloride solution. Washing the cobaltous oxalate by standard techniques such as with water or dilute acids and bases prior to pyrolysis does not reduce the impurities in the cobaltous oxalate and the impurities are therefore carried over to the cobalt metal. Such impurities render the metal powder unuseful for some applications such as in the hard carbide industry, and therefore the value of the cobalt is lowered.
A process for purifying cobaltous oxalate or other cobalt salt prior to conversion to cobalt metal would therefore be desirable.
The following U.S. Patents relate to cobalt processing: U.S. Pat. No. 4,184,868 relates to a method for producing extra fine cobalt metal powder by digesting cobalt pentammine chloride in ammonium hydroxide to obtain a black precipitate which contains cobalt and which is thereafter reduced to the metal powder. U.S. Pat. Nos. 4,214,894, 4,233,063, and 4,278,463 relate to improvements in 4,184,868 in which the ammonia solutions are processed to recover any cobalt therein. U.S. Pat. Nos. 4,395,278 and 4,469,505 relate to improvements in 4,184,868 in which fine cobalt metal powder is produced having reduced tailings.
U.S. Pat. No. 4,214,895 relates to a process for producing cobalt metal powder which involves treating an aqueous solution of a soluble cobaltic ammine halide with a sufficient amount of a soluble metallic hydroxide to form a cobalt containing precipitate which is thereafter reduced to metallic cobalt.
U.S. Pat. No. 4,218,240 relates to a method for producing cobalt metal powder by forming a solution of a cobalt hexammine compound from an acid solution and treating the solution with a metallic hydroxide to form a precipitate which is reduced to cobalt metal powder. U.S. Pat. Nos. 4,348,224 and 4,381,937 relate to improvememts in the process described in 4,218,240 which involve removal of copper and silver from the cobalt. U.S. Pat. No. 4,452,633 relates to an improvement in the process described in 4,218,240 and 4,348,224 in which the silver is recovered.
U.S. Pat. No. 4,329,169 relates to a process for producing fine particle size cobalt metal powder absent tailings by heating an aqueous solution of soluble cobalt ammine halide to decompose the halide and form a cobalt containing precipitate which is reduced to the cobalt metal powder.
U.S. Pat. No. 4,409,019 relates to a process for producing fine cobalt metal powder from pieces of relatively pure cobalt by dissolving the cobalt pieces in an aqueous solution of hydrogen iodide and iodine and forming a cobalt containing solid which is subsequently reduced to a fine cobalt metal powder.